1. Field of the Invention
The present invention generally relates to an electrophotographic copying machine and, more particularly, to the electrophotographic copying machine, or multi-color copying machine, capable of reproducing an image in a plurality of colors.
2. Description of the Prior Art
An example of multi-color copying machine is disclosed in the Japanese Laid-open Pat. Publication No.61-203474. The multi-color copying machine disclosed therein is so designed that a plurality of developing units accommodating therein respective masses of powdery developers of different colors can be selectively driven in association with a particular copying area specified by means of an image editing means to accomplish a multi-color copying during one cycle of copying operation.
The developing units according to the above mentioned publication are arranged one after another in a direction conforming to the direction of rotation of a photoreceptor drum, and control is made so that the developing units can be selectively driven or halted in synchronism with the arrival of an electrostatic latent image on the photoreceptor drum, which corresponds to the boundary of the copying area so specified, at an associated developing area.
It has, however, been found that, when control is made to stop the drive of the first developing unit relative to the boundary of the specified copying area, that is, a developer switching position, and to start the drive of the other developing unit, an color mixed area necessarily occurs at an overlapping region between an set-up portion and a set-down portion as shown in FIG. 8. The occurrence of the color mixed area brings about reduction in quality of the resultant color copy and, at the same time, constitutes a cause of incapability of providing a clear color copy because the powdery developer contained in the first developing unit tends to be drawn into and mixed with the powdery developer in the other developing unit.